... Just keep in mind that you can do this before each of the cards you could play from your hand which can result in some long chains of selling and buying.
Thank you! I think this answers my question!
So you are allowed to sell/buy goods, play a card and then sell/buy goods again before playing the next card this turn.
At first I thought that you were allowed to sell/buy goods only before playing your first card in the turn (this way you should plan ahead what you will need during the round).
Regarding the use of the cards, we played it correctly: each card can be used only once. But if you have, for example, 5 copied of the same card in your hand (let's say 5 copies of food->metal) you then should be able to:
1- buy food
2- convert food in metal with your first card (scoring 3 points)
3- sell the just produced metal and buy new food
4- play your second card to convert food in metal (scoring other 3 points)